Dry electrophotographic copiers and printers develop an image utilizing a dry toner. The typical toner is composed of styrene acrylic resin, a pigment-typically carbon black, and a charge control dye to endow the toner with the desired tribocharging properties for developing a latent electrostatic image. Styrene acrylic resin is a thermo-plastic which can be melted and fused to the desired medium, typically paper.
The typical fusing system in an electrophotographic printer or copier is composed of two heated platen rollers which, when print media with a developed image pass between them, melt the toner and through pressure physically fuse the molten thermal plastic to the medium. Heating is usually accomplished by placing one or more high power tungsten filament quartz lamps inside the hollow platen roller.
These types of printers or copiers, however, tend to suffer from phenomenon know as “flicker.” Flicker is measured by the proposed European regulatory document IEC 61000-3-3, and is the impression of unsteadiness of visual sensation induced by a light stimulus whose luminance or spectral distribution fluctuates with time. In electrical power distribution systems, flicker is the result of large current changes reacting with the power distribution system impedance causing voltage fluctuations. These voltage fluctuations, in the form of voltage sags and surges, cause the light output of incandescent lamps to fluctuate and can cause fluorescent lamps to drop out. Flicker in incandescent lamps is easily noticed because photonic emissions for incandescent lamps is a nonlinear function of the voltage source and any voltage deviation causes a much larger deviation in the luminescent intensity of the light emitted from the incandescent lamp. Light flicker is visually irritating and also represents unwanted harmonics and power transients being placed on a power system.
Many printer and copiers on the market today are based on what shall be referred to as “triac control”. In order to better understand this so called “triac control”, reference is made to FIG. 1 which shows in block diagram form the arrangement of the basic type of triac controlled arrangement.
As shown in FIG. 1, an AC voltage source is connected to a fuser resistor which generates heat, by way of a triac. The triac is controlled by a circuit (viz., a microprocessor) that implements a power control algorithm via which the phase angle of the triac (φ) is determined based on inputs from a zero cross detection circuit, a circuit which monitors the phase angle of the AC current being fed to the fuser, a temperature set point circuit, and a temperature sensor signal indicative of the temperature of the fuser. The inputs from the temperature set point circuit and the temperature indicative signal from the fuser are monitored via suitable control routines and when the temperature of the fuser of the fusing system exceeds the set point temperature, the gate signal (which takes the form of a narrow pulse whose duty ratio, d, is less than 1%), is stopped.
As will be understood, the current flow through the triac which is initiated by the narrow gate pulse, extinguishes when the current flow, which passes therethrough as a result of the gate opening pulse, falls below a minimum holding current which is necessary to keep the triac conducting.
The power p(d) which is delivered is given by:       p    ⁡          (      d      )        :=            1      π        ·                  V        2            R        ·          (                        d          ·                      π            2                          -                              1            2                    ·                      sin            ⁡                          (                              d                ·                π                            )                                ·                      cos            ⁡                          (                              d                ·                π                            )                                          )      wherein:                V:=peak AC voltage;        d:=duty ratio (the fraction of the half cycle for which the triac conducts); and        R:=resistance in ohms.        
However, it should be noted that the AC current which is drawn by the above described type of phase controlled triac is rich in harmonics.